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USB: fix comment about endianness of descriptors

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This patch fixes a comment and clarifies the documentation about the
endianness of descriptors. The current policy is that descriptors will
be little-endian at the API even on big-endian systems; however the
/proc/bus/usb API predates this policy and presents descriptors with
some multibyte fields byte-swapped.

Signed-off-by: Phil Endecott <usb_endian_patch@chezphil.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Phil Endecott 2008-12-01 10:22:33 -05:00 • committed by Greg Kroah-Hartman
parent c33ba39214
commit 9a9fafb894
2 changed files with 10 additions and 4 deletions
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8
include/linux/usb/ch9.h
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@ -158,8 +158,12 @@ struct usb_ctrlrequest {
* (rarely) accepted by SET_DESCRIPTOR.
*
* Note that all multi-byte values here are encoded in little endian
* byte order "on the wire". But when exposed through Linux-USB APIs,
* they've been converted to cpu byte order.
* byte order "on the wire". Within the kernel and when exposed
* through the Linux-USB APIs, they are not converted to cpu byte
* order; it is the responsibility of the client code to do this.
* The single exception is when device and configuration descriptors (but
* not other descriptors) are read from usbfs (i.e. /proc/bus/usb/BBB/DDD);
* in this case the fields are converted to host endianness by the kernel.
*/
/*